IL-4/ IL-13 directed microglial activation and differentiation in response to LPS-induced neuroinflammation

Microglia activation is a common hallmark of neuroinflammation that occurs during pathogen invasion or lipopolysaccharide (LPS)-induced inflammation. A neuroinflammatory response is elicited by the release of proinflammatory cytokines which stimulates microglia in an autocrine manner to be polarized into classically activated, pro-inflammatory M1 cells. Prolonged exposure to the inflammatory response can have disastrous effects on the central nervous system (CNS). However, microglia can alternatively be polarized into the activated M2 anti-inflammatory phenotype, but the exact molecular mechanism mediating this phenotypic switch remains poorly understood. Studies have shown that interleukin (IL)-4 can induce the M2 phenotype and activate the signal transducer and activator of the transcription 6 (STAT6) signalling pathway that in turn provokes a beneficial Th2 immune response. Since IL-4 and IL-13 share a common IL-4 receptor alpha (IL-4Rα) chain, it is possible that alternative microglia differentiation and its anti-inflammatory action also involve IL-13. This study aimed to investigate how IL-13 and STAT6 signalling orchestrates the microglial response and differentiation associated with LPS-induced inflammation. Furthermore, the molecular mechanisms that relieve LPS-induced neuroinflammation and neural protection through IL-13-enhanced BDNF signalling were also investigated. C8-B4 microglial cells were induced with LPS to exhibit an M1 pro-inflammatory phenotype or stimulated with IL-4 and/or IL-13 to exhibit an M2 anti-inflammatory microglial phenotype. The cell viability following LPS, IL-4, and/ or IL-13 exposure was determined. The LPS-induced neuroinflammatory response and the anti-inflammatory response induced by IL-4 and IL-13 which promotes STAT-6 signalling were determined by measuring TNFα, IL-1β, and BDNF protein concentrations using ELISA assays. The polarising effects of LPS and IL-4/IL-13 cytokines were also examined via changes in the expression of Iba-1, CD206, CD86, and STAT-6 determined by immunofluorescence analysis. These changes were further investigated by quantifying the mRNA transcripts of TNFα, IL-1 β, Arg-1, CD206, IL-4R, and STAT-6 and BDNF using qRT-PCR.Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 202